Alterations of HLA class I expression in human melanoma xenografts in immunodeficient mice occur frequently and are associated with higher tumorigenicity

Immunotherapy in melanoma: advances, pitfalls, and future perspectives

Cutaneous melanoma is the deadliest and most aggressive form of skin cancer owing to its high capacity for metastasis. Over the past few decades, the management of this type of malignancy has undergone a significant revolution with the advent of both targeted therapies and immunotherapy, which have greatly improved patient quality of life and survival. Nevertheless, the response rates are still unsatisfactory for the presence of side effects and development of resistance mechanisms. In this context, tumor microenvironment has emerged as a factor affecting the responsiveness and efficacy of immunotherapy, and the study of its interplay with the immune system has offered new promising clinical strategies. This review provides a brief overview of the currently available immunotherapeutic strategies for melanoma treatment by analyzing both the positive aspects and those that require further improvement. Indeed, a better understanding of the mechanisms involved in the immune evasion of melanoma cells, with particular attention on the role of the tumor microenvironment, could provide the basis for improving current therapies and identifying new predictive biomarkers.

MHC heterogeneity and response of metastases to immunotherapy

In recent years, immunotherapy has proven to be an effective treatment against cancer. Cytotoxic T lymphocytes perform an important role in this anti-tumor immune response, recognizing cancer cells as foreign, through the presentation of tumor antigens by MHC class I molecules. However, tumors and metastases develop escape mechanisms for evading this immunosurveillance and may lose the expression of these polymorphic molecules to become invisible to cytotoxic T lymphocytes. In other situations, they may maintain MHC class I expression and promote immunosuppression of cytotoxic T lymphocytes. Therefore, the analysis of the expression of MHC class I molecules in tumors and metastases is important to elucidate these escape mechanisms. Moreover, it is necessary to determine the molecular mechanisms involved in these alterations to reverse them and recover the expression of MHC class I molecules on tumor cells. This review discusses the role and regulation of MHC class I expression in tumor progression. We focus on altered MHC class I phenotypes present in tumors and metastases, as well as the molecular mechanisms responsible for MHC-I alterations, emphasizing the mechanisms of recovery of the MHC class I molecules expression on cancer cells. The individualized study of the HLA class I phenotype of the tumor and the metastases of each patient will allow choosing the most appropriate immunotherapy treatment based on a personalized medicine.

Restoration of MHC-I on Tumor Cells by Fhit Transfection Promotes Immune Rejection and Acts as an Individualized Immunotherapeutic Vaccine

The capacity of cytotoxic-T lymphocytes to recognize and destroy tumor cells depends on the surface expression by tumor cells of MHC class I molecules loaded with tumor antigen peptides. Loss of MHC-I expression is the most frequent mechanism by which tumor cells evade the immune response. The restoration of MHC-I expression in cancer cells is crucial to enhance their immune destruction, especially in response to cancer immunotherapy. Using mouse models, we recovered MHC-I expression in the MHC-I negative tumor cell lines and analyzed their oncological and immunological profile. Fhit gene transfection induces the restoration of MHC-I expression in highly oncogenic MHC-I-negative murine tumor cell lines and genes of the IFN-γ transduction signal pathway are involved. Fhit-transfected tumor cells proved highly immunogenic, being rejected by a T lymphocyte-mediated immune response. Strikingly, this immune rejection was more frequent in females than in males. The immune response generated protected hosts against the tumor growth of non-transfected cells and against other tumor cells in our murine tumor model. Finally, we also observed a direct correlation between FHIT expression and HLA-I surface expression in human breast tumors. Recovery of Fhit expression on MHC class I negative tumor cells may be a useful immunotherapeutic strategy and may even act as an individualized immunotherapeutic vaccine.

Cancer immunoediting and resistance to T cell-based immunotherapy

Anticancer immunotherapies involving the use of immune-checkpoint inhibitors or adoptive cellular transfer have emerged as new therapeutic pillars within oncology. These treatments function by overcoming or relieving tumour-induced immunosuppression, thereby enabling immune-mediated tumour clearance. While often more effective and better tolerated than traditional and targeted therapies, many patients have innate or acquired resistance to immunotherapies. Cancer immunoediting is the process whereby the immune system can both constrain and promote tumour development, which proceeds through three phases termed elimination, equilibrium and escape. Throughout these phases, tumour immunogenicity is edited, and immunosuppressive mechanisms that enable disease progression are acquired. The mechanisms of resistance to immunotherapy seem to broadly overlap with those used by cancers as they undergo immunoediting to evade detection by the immune system. In this Review, we discuss how a deeper understanding of the mechanisms underlying the cancer immunoediting process can provide insight into the development of resistance to immunotherapies and the strategies that can be used to overcome such resistance.

Multiple immunofluorescence assay identifies upregulation of Active β-catenin in prostate cancer

Objectives

To apply a systems pathology-based approach to the quantification of nuclear Active β-catenin and human leukocyte antigen class I, and assess the biomarker involvement in a cohort of prostate tumor patients.

Results

The systems pathology approach applied allows a precise quantification of the marker expression in the different cell compartments as well as the determination of the areas that coexpress two markers. Our data shows that the accumulation of β-catenin in the nuclear compartment is significantly decreased in the adjacent normal areas when compared to tumor of the same patients (p < 0.001). In conclusion, the application of this novel multiple immunofluorescence assay demonstrates that the upregulation of Active β-catenin is a relatively common feature of prostate tumor development, and further supports the activation of the Wnt/β-catenin pathway in prostate cancer progression.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4100-z) contains supplementary material, which is available to authorized users.

MHC Intratumoral Heterogeneity May Predict Cancer Progression and Response to Immunotherapy

An individual tumor can present intratumoral phenotypic heterogeneity, containing tumor cells with different phenotypes that do not present irreversible genetic alterations. We have developed a mouse cancer model, named GR9, derived from a methylcholanthrene-induced fibrosarcoma that was adapted to tissue culture and cloned into different tumor cell lines. The clones showed diverse MHC-I phenotypes, ranging from highly positive to weakly positive MHC-I expression. These MHC-I alterations are due to reversible molecular mechanisms, because surface MHC-I could be recovered by IFN-γ treatment. Cell clones with high MHC-I expression demonstrated low local oncogenicity and high spontaneous metastatic capacity, whereas MHC-I-low clones showed high local oncogenicity and no spontaneous metastatic capacity. Although MHC-I-low clones did not metastasize, they produced MHC-I-positive dormant micrometastases controlled by the host immune system, i.e., in a state of immunodormancy. The metastatic capacity of each clone was directly correlated with the host T-cell subpopulations; thus, a strong decrease in cytotoxic and helper T lymphocytes was observed in mice with numerous metastases derived from MHC-I positive tumor clones but a strong increase was observed in those with dormant micrometastases. Immunotherapy was administered to the hosts after excision of the primary tumor, producing a recovery in their immune status and leading to the complete eradication of overt spontaneous metastases or their decrease. According to these findings, the combination of MHC-I surface expression in primary tumor and metastases with host T-cell subsets may be a decisive indicator of the clinical outcome and response to immunotherapy in metastatic disease, allowing the identification of responders to this approach.

Emerging therapies provide new opportunities to reshape the multifaceted interactions between the immune system and lymphoma cells

The acquisition of a complete neoplastic phenotype requires cancer cells to develop escape mechanisms from the host immune system. This phenomenon, commonly referred to as 'immune evasion,' represents a hallmark of cancers and results from a Darwinian selection of the fittest tumor clones. First reported in solid tumors, cancer immunoescape characterizes several hematological malignancies. The biological bases of cancer immunoescape have recently been disclosed and include: (i) impaired human leukocyte antigen-mediated cancer cell recognition (B2M, CD58, CTIIA, CD80/CD86, CD28 and CTLA-4 mutations); (ii) deranged apoptotic mechanisms (reduced pro-apoptotic signals and/or increased expression of anti-apoptotic molecules); and (iii) changes in the tumor microenvironment involving regulatory T cells and tumor-associated macrophages. These immune-escape mechanisms characterize both Hodgkin and non-Hodgkin (B and T cell) lymphomas and represent a promising target for new anti-tumor therapies. In the present review, the principles of cancer immunoescape and their role in human lymphomagenesis are illustrated. Current therapies targeting these pathways and possible applications for lymphoma treatment are also addressed.

Histone Modifications, Modifiers and Readers in Melanoma Resistance to Targeted and Immune Therapy

The treatment of melanoma has been revolutionized by new therapies targeting MAPK signaling or the immune system. Unfortunately these therapies are hindered by either primary resistance or the development of acquired resistance. Resistance mechanisms involving somatic mutations in genes associated with resistance have been identified in some cases of melanoma, however, the cause of resistance remains largely unexplained in other cases. The importance of epigenetic factors targeting histones and histone modifiers in driving the behavior of melanoma is only starting to be unraveled and provides significant opportunity to combat the problems of therapy resistance. There is also an increasing ability to target these epigenetic changes with new drugs that inhibit these modifications to either prevent or overcome resistance to both MAPK inhibitors and immunotherapy. This review focuses on changes in histones, histone reader proteins and histone positioning, which can mediate resistance to new therapeutics and that can be targeted for future therapies.

Epigenetic changes within the promoter regions of antigen processing machinery family genes in Kazakh primary esophageal squamous cell carcinoma

The esophageal squamous cell carcinoma (ESCC) is thought to develop through a multi-stage process. Epigenetic gene silencing constitutes an alternative or complementary mechanism to mutational events in tumorigenesis. Posttranscriptional regulation of human leukocyte antigen class I (HLA-I) and antigen processing machinery (APM) proteins expression may be associated with novel epigenetic modifications in cancer development. In the present study, we determined the expression levels of HLA-I antigen and APM components by immunohistochemistry. Then by a bisulfite-sequencing PCR (BSP) approach, we identified target CpG islands methylated at the gene promoter region of APM family genes in a ESCC cell line (ECa109), and further quantitative analysis of CpG site specific methylation of these genes in cases of Kazakh primary ESCCs with corresponding non-cancerous esophageal tissues using the Sequenom MassARRAY platform. Here we showed that the development of ESCCs was accompanied by partial or total loss of protein expression of HLA-B, TAP2, LMP7, tapasin and ERp57. The results demonstrated that although no statistical significance was found of global target CpG fragment methylation level sof HLA-B, TAP2, tapasin and ERp57 genes between ESCC and corresponding non-cancerous esophageal tissues, there was significant differences in the methylation level of several single sites between the two groups. Of thesse only the global methylation level of LMP7 gene target fragments was statistically higher (0.0517±0.0357) in Kazakh esophageal cancer than in neighboring normal tissues (0.0380±0.0214, p<0.05). Our results suggest that multiple CpG sites, but not methylation of every site leads to down regulation or deletion of gene expression. Only some of them result in genetic transcription, and silencing of HLA-B, ERp57, and LMP7 expression through hypermethylation of the promoters or other mechanisms may contribute to mechanisms of tumor escape from immune surveillance in Kazakh esophageal carcinogenesis.

T lymphocytes restrain spontaneous metastases in permanent dormancy

Tumor dormancy is a clinical phenomenon related to immune equilibrium during cancer immunoediting. The mechanisms involved in dormant metastases are poorly understood due to the lack of preclinical models. Here, we present a nontransgenic mouse model in which spontaneous metastases remain in permanent immunomediated dormancy with no additional antitumor treatment. After the injection of a GR9-B11 mouse fibrosarcoma clone into syngeneic BALB/c mice, all animals remained free of spontaneous metastases at the experimental endpoints (3-8 months) but also as long as 24 months after tumor cell injection. Strikingly, when tumor-bearing mice were immunodepleted of T lymphocytes or asialo GM1-positive cells, the restraint on dormant disseminated metastatic cells was relieved and lung metastases progressed. Immunostimulation was documented at both local and systemic levels, with results supporting the evidence that the immune system was able to restrain spontaneous metastases in permanent dormancy. Notably, the GR9-B11 tumor clone did not express MHC class I molecules on the cell surface, yet all metastases in immunodepleted mice were MHC class I-positive. This model system may be valuable for more in-depth analyses of metastatic dormancy, offering new opportunities for immunotherapeutic management of metastatic disease.

Preclinical modeling of EGFR-specific antibody resistance: oncogenic and immune-associated escape mechanisms

To define the molecular basis of secondary resistance to epidermal growth factor receptor (EGFR)-specific antibodies is crucial to increase clinical benefit in patients. The limited access to posttreatment tumor samples constitutes the major barrier to conduct these studies, representing preclinical experimentation as a useful alternative. Anti-EGFR antibody-based therapy has been reported to mediate tumor regression by interrupting oncogenic signals and, more recently, by inducing antitumor immunological responses. However, resistance models have been focused only on tumor escape associated with EGFR blockade, whereas studies describing immune-associated escape mechanisms have not been reported thus far. To address this idea, we modeled resistance induction in D122 metastasis-bearing C57BL/6 mice treated with 7A7 (an anti-murine EGFR antibody). Similarly to patients receiving EGFR-specific antibodies, 7A7 resistance promotion represents an important drawback to successful therapy. Characterization of primary cultures derived from metastasis in 7A7-treated mice revealed a high frequency of tumor variants resistant to in vivo and in vitro antibody treatment. We showed, for the first time, the convergence of alterations in oncogenic and immunological pathways in 7A7-resistant variants. To identify key molecules behind resistance, seven 7A7-resistant variants were screened. HER3 overexpression and PTEN deficiency leading to hyperactivation of protumoral downstream signaling were found in these variants as a consequence of 7A7-mediated EGFR inhibition. Concomitantly, we found a high percentage of resistant variants carrying abnormalities in the constitutive and/or interferon gamma (IFN-γ)-inducible major histocompatibility complex I (MHC-I) expression. A significant decrease in mRNA levels for MHC-I heavy chains, β2-microglogulin and antigen processing machinery genes as well as transcriptional alterations in IFN-γ pathway components were identified as the main mechanisms underlying MHC-I expression defects in 7A7-resistant variants. Notably, these defects have not been previously associated with EGFR-specific antibody resistance, providing novel immunological escape mechanisms. This study has strong implications for the development of new combination strategies to overcome anti-EGFR antibodies refractoriness.

LOH in the HLA class I region at 6p21 is associated with shorter survival in newly diagnosed adult glioblastoma

PURPOSE

Glioblastoma (GBM) shows downregulated expression of human leukocyte antigen (HLA) class I, thereby escaping from cytotoxic T cells and limiting the efficacy of immunotherapy. Loss of heterozygosity (LOH) of HLA class I (6p21) and/or β-2 microglobulin (B2m) (15q21) regions represents irreversible downregulation. In this study, we examined the prevalence of these LOH events and their relations with overall survival in GBM.

EXPERIMENTAL DESIGN

In a cross-sectional analysis on 60 adult patients with GBM, DNA from formalin-fixed, paraffin-embedded specimens were evaluated for 10 microsatellite regions of HLA class I, B2m, HLA class II, HLA class III, and 6q by PCR as well as immunohistochemical evaluation of HLA class I expression and CD8(+) T-cell infiltration.

RESULTS

LOH in HLA class I, B2m, HLA class II, HLA class III, and 6q regions was present in 41.4%, 18.2%, 9.4%, 77.8%, and 36.0% of informative cases, respectively. LOH of HLA class I was associated with shorter overall survival (HR = 4.89, P = 0.0078). HLA class I was downregulated in 22% to 43% of cases based on immunohistochemistry. Cases that displayed negative staining were significantly younger. HLA class I expression correlated with intratumoral CD8(+) T-cell infiltration.

CONCLUSION

LOH in the HLA class I region is frequent in adult GBMs. The association of shorter survival with LOH in this region suggests a crucial role for these genes in immunosurveillance.

Lessons from cancer immunoediting in cutaneous melanoma

We will revisit the dual role of the immune system in controlling and enabling tumor progression, known as cancer immunoediting. We will go through the different phases of this phenomenon, exposing the most relevant evidences obtained from experimental models and human clinical data, with special focus on Cutaneous Melanoma, an immunogenic tumor per excellence. We will describe the different immunotherapeutic strategies employed and consider current models accounting for tumor heterogeneity. And finally, we will propose a rational discussion of the progress made and the future challenges in the therapeutics of Cutaneous Melanoma, taking into consideration that tumor evolution is the resulting from a continuous feedback between tumor cells and their environment, and that different combinatorial therapeutic approaches can be implemented according to the tumor stage.

The tumour suppressor Fhit positively regulates MHC class I expression on cancer cells

MHC class I (MHC-I) molecules are ubiquitously expressed on the cells of an organism. Study of the regulation of these molecules in normal and disease conditions is important. In tumour cells, the expression of MHC-I molecules is very frequently lost, allowing these cells to evade the immune response. Cancers of different histology have shown total loss of MHC-I molecule expression, due to a coordinated transcriptional down-regulation of various antigen-processing machinery (APM) components and/or MHC-I heavy chains. The mechanisms responsible for these alterations remain unclear. We determined the possible genes involved by comparing MHC-I-positive with MHC-I-negative murine metastases derived from the same fibrosarcoma tumour clone. MHC-I-negative metastases showed transcriptional down-regulation of APM and MHC-I heavy chains. The use of microarrays and subtraction cDNA libraries revealed four candidate genes responsible for this alteration, but two of them were ruled out by real-time RT-PCR analyses. The other two genes, AP-2α and Fhit tumour suppressors, were studied by using siRNA to silence their expression in a MHC-I-positive metastatic cell line. AP-2α inhibition did not modify transcriptional expression of APM components or MHC-I heavy chains or surface expression of MHC-I. In contrast, silencing of the Fhit gene produced the transcriptional down-regulation of APM components and MHC-I heavy chains and decreased MHC-I surface expression. Moreover, transfection of Fhit in MHC-I-negative tumour cell lines restored MHC-I cell surface expression. These data indicate that defects in Fhit expression may promote MHC-I down-regulation in cancer cells and allow escape from immunosurveillance(#).

The role of classical and non-classical HLA class I antigens in human tumors

In human tumors alterations in the surface expression and/or function of the major histocompatibility complex (MHC) class I antigens are frequently found and equip neoplastic cells with mechanisms to escape immune control. The aberrant expression of HLA class I molecules can be caused by structural alterations or dysregulations of genes encoding the classical HLA class I antigens and/or components of the HLA class I antigen processing machinery (APM). The dysregulation of APM components could occur at the epigenetic, transcriptional or post-transcriptional level. In some malignancies these abnormalities are significantly associated with a higher tumor staging, grading, disease progression and a reduced survival of patients as well as a failure to CD8(+) T cell-based immunotherapies. In addition to HLA class I abnormalities, expression of the non-classical HLA-G antigen is often induced in tumors, which could be mediated by various microenvironmental factors. Interestingly, soluble HLA-G serum and plasma levels have been useful markers for the prediction of some malignancies. The biological consequence of HLA-G expression or sHLA-G is an escape from T and NK cell-mediated recognition. Thus, alterations of non-classical and classical HLA class I antigens and components of the antigen processing pathway provide tumor cells with different mechanisms to inactivate immune responses resulting in tumor growth and evasion from host immune surveillance.

Novel insights into the molecular mechanisms of HLA class I abnormalities

Alterations in the MHC class I surface antigens represent one mechanism of tumor cells to escape from natural or immunotherapy-induced antitumor immune responses. In order to restore MHC class I expression, knowledge about the underlying molecular mechanisms of MHC class I defects in different tumor types is required. In most cases, abnormalities of MHC class I expression are reversible by cytokines suggesting a deregulation rather than structural abnormalities of members of the antigen-processing and presentation machinery (APM). The impaired expression of APM components could be controlled at the epigenetic, transcriptional and/or posttranscriptional level. Furthermore, a direct link between altered transcription factor binding, interferon signal transduction and MHC class I APM component expression has been shown, which might be further associated with cell cycle progression. This information will not only give novel insights into the (patho) physiology of the antigen-processing and presenting pathway, but will help in the future to design effective T cell-based immunotherapies.

MHC class I molecules act as tumor suppressor genes regulating the cell cycle gene expression, invasion and intrinsic tumorigenicity of melanoma cells

The alteration of MHC class I (MHC-I) expression is a frequent event during cancer progression, allowing tumor cells to evade the immune system. We report that the loss of one major histocompatibility complex haplotype in human melanoma cells not only allowed them to evade immunosurveillance but also increased their intrinsic oncogenic potential. A second successive defect in MHC-I expression, MHC-I total downregulation, gave rise to melanoma cells that were more oncogenic per se in vivo and showed a higher proliferation rate and greater migratory and invasive potential in vitro. All these processes were reversed by restoring MHC-I expression via human leukocite antigen-A2 gene transfection. MHC-I cell surface expression was inversely correlated with intrinsic oncogenic potential. Modifications in the expression of various cell cycle genes were correlated with changes in MHC-I expression; the most important differences among the melanoma cell lines were in the transcriptional level of AP2-alpha, cyclin A1 and p21WAF1/CIP1. According to these results, altered MHC-I expression in malignant cells can directly increase their intrinsic oncogenic and invasive potential and modulate the expression of cell cycle genes. These findings suggest that human leukocite antigen class I molecules may act directly as tumor suppressor genes in melanoma.

Differential down-modulation of HLA class I and II molecule expression on human tumor cell lines upon in vivo transfer

Previous evidence from our laboratory showed that Epstein–Barr virus–immortalized lymphoblastoid B cells undergo a prominent down-modulation of HLA-II molecule expression when injected intraperitoneally in SCID mice, while HLA-I remains almost unaffected. Since this phenomenon can alter the experimental outcome of therapeutic protocols of adoptive cell therapy, we decided to evaluate the behavior of MHC antigens in a panel of cell lines belonging to the B- and T-cell lineages, as well as in epithelial tumor cell lines. Cells were administered in mice either intraperitoneally or subcutaneously and recovered 4 days later for HLA molecule expression analysis. Collected data showed a highly heterogeneous in vivo behavior of the various cell lines, which could alternatively down-modulate, completely abrogate or maintain unchanged the expression of either MHC-I or MHC-II molecules. Moreover, the site of injection impacted differentially on these aspects. Although such phenomena still lack a comprehensive clarification, epigenetic mechanisms are likely to be involved as epigenetic drugs could partially counteract MHC down-modulation in vivo. Nonetheless, it has to be pointed out that careful attention must be paid to the assessment of therapeutic efficacy of translational protocols of adoptive immunotherapy, as modulation of MHC molecules on human target cells when transferred in a mouse environment could readily interfere with the desired and expected therapeutic effects.

Ten years of progress in vaccination against cancer: the need to counteract cancer evasion by dual targeting in future therapies

Although cancer immunology has made vigorous progress over the last decade, its future remains uncertain. Tumors have clearly proved subject to immune surveillance, leading to antigenic editing, and means of activating both T and B arms of the immune system have been devised. Therapeutic vaccination and monoclonal antibody therapy have so far proved disappointing, because tumors prove adept at evasion from immune control. Dual targeting could well counteract evasion, provided that the two targets are independent and are attacked simultaneously. This stage has nearly but not quite been reached in several forms of immunotherapy, particularly of B-cell cancers, although such treatment also carries hazards.

Identification of E2F1 as an important transcription factor for the regulation of tapasin expression

HER-2/neu overexpression in tumor cells caused abnormalities of MHC class I surface expression due to impaired expression of components of the antigen-processing machinery (APM) including the low molecular weight proteins, the transporter associated with antigen processing (TAP), and the chaperone tapasin, whereas the expression of MHC class I heavy chain as well as β(2)-microglobulin was only marginally affected. This oncogene-mediated deficient APM component expression could be reverted by interferon-γ treatment, suggesting a deregulation rather than structural alterations as underlying molecular mechanisms. To determine the level of regulation, the transcriptional activity of APM components was analyzed in HER-2/neu(-) and HER-2/neu(+) cells. All major APM components were transcriptionally down-regulated in HER-2/neu(+) when compared with HER-2/neu(-) cells, which was accompanied by a reduced binding of RNA polymerase II to the APM promoters. Site-directed mutagenesis of the p300- and E2F-binding sites in the APM promoters did not reconstitute the oncogene-mediated decreased transcription rate with the exception of tapasin, which was restored in HER-2/neu(+) cells to levels of wild type tapasin promoter activity in HER-2/neu(-) fibroblasts. The E2F-directed control of tapasin expression was further confirmed by chromatin immunoprecipitation analyses showing that E2F1 and p300 bind to the tapasin and APM promoters in both cell lines. Moreover, siRNA-mediated silencing of E2F1 was associated with an increased tapasin expression, whereas transient overexpression of E2F1 launch a reduced tapasin transcription, suggesting that E2F1 is an essential transcription factor for tapasin.

Tumor-mediated inhibition of dendritic cell differentiation is mediated by down regulation of protein kinase C beta II expression

Tumor-mediated immune suppression occurs through multiple mechanisms, including dysregulation of dendritic cell differentiation. This block in differentiation results in fewer dendritic cells and an accumulation of immunosuppressive myeloid- derived suppressor cells and is thought to contribute to tumor outgrowth and to act as an impediment to successful anti-cancer immunotherapy. Tumor-mediated myeloid dysregulation is known to be Stat3 dependent; however, the molecular mechanism of this Stat3 signaling remains poorly defined. We have previously shown that PKC betaII is required for dendritic cell differentiation. Here, we describe our finding that tumors mediate both Stat3 activation and PKC betaII down regulation in DC progenitor cells, a process mimicked by the expression of a constitutive active Stat3 mutant. This demonstrates that tumor-mediated myeloid dysregulation may be mediated by Stat3- induced PKC betaII down regulation.

Inhibition of p-STAT3 enhances IFN-alpha efficacy against metastatic melanoma in a murine model

PURPOSE

Melanoma is a common and deadly tumor that upon metastasis to the central nervous system has a median survival duration of <6 months. Activation of the signal transducer and activator of transcription 3 (STAT3) has been identified as a key mediator that drives the fundamental components of melanoma malignancy, including immune suppression in melanoma patients. We hypothesized that WP1193, a novel inhibitor of STAT3 signaling, would enhance the antitumor activity of IFN-alpha against metastatic melanoma.

EXPERIMENTAL DESIGN

Combinational therapy of STAT3 blockade agents with IFN-alpha was investigated in a metastatic and an established syngeneic intracerebral murine tumor model of melanoma. The immunologic in vivo mechanisms of efficacy were investigated by T-cell and natural killer (NK) cell cytotoxic assays.

RESULTS

IFN-alpha immunotherapy was synergistic with WP1193 showing marked in vivo efficacy against metastatic and established intracerebral melanoma. At autopsy, it was noted that there was a decreased trend in mice with melanoma developing leptomeningeal disease treated with combinational therapy. The combinational approach enhanced both NK-mediated and T-cell-mediated antitumor cytotoxicity.

CONCLUSIONS

The immune modulatory effects of STAT3 blockade can enhance the therapeutic efficacy of IFN-alpha immunotherapy by enhancing both innate and adaptive cytotoxic T-cell activities. This combination therapy has the potential in the treatment of metastatic melanoma that is typically refractory to this type of immune therapeutic approach.